US2420291A - Electrodepositing copper upon steel wire - Google Patents

Description

y 1 47- o. E. ADLER 2,420,291

ELBG'I'RODBPOSITING COPPER UPON STBBL IIRE Filed July 22. 1940 & i 6% W48,

Patented May 13, 1947 ELECTRODEPOSITING COPPER UPON STEEL WIRE Orville E. Adler, Niles, Mich., assignor to National-Standard Company, a corporation of Michigan Application July 22, 1940, Serial No. 346,867

6 Claims. (01. 204-34) This invention relates to a method of producing a copper clad wire, and particularly a copper clad steel wire of very high tensile strength, which has been drawn after the application of the copper to it.

Copper clad steel wires heretofore have been prepared in two different ways. In the earlier method a casting was prepared in which a large body of copper surrounded a billet or rod of steel. The whole material was reduced to the proper size. It has also been suggested to electroplate copper directly upon a finished wire.

Both of these methods were unsatisfactory for various reasons. The direct electroplating of copper upon a wire has lately come into favor, but this method is expensive. It does not result in uniform copper coatings, and the wires necessarily employed for direct plating have a very low tensile strength.

In accordance with the present invention, a copper clad wire of higher tensile strength than those previously produced and at the same time having a copper coating of great uniformity is produced.

The invention is illustrated diagrammatically in the drawings, in which: Figure 1 represents a cross section of wire before drawing; and Figure 2 is a cross section of the wire after drawing.

The wire employed is preferably a high tensile strength, high carbon wire, for example, one

having a typical composition as follows:

Balance is iron, with cases of impurities.

The wire must be carefully cleaned before treatment. The following example illustrates a typical treatment for a 0.119 inch diameter wire of the above composition which has been patented and limed.

Wire having a diameter of 0.185 inch and of the same composition as the wire heretofore described, and double lead patented, was cleaned in 32% hydrochloric acid at a temperature of 150 F. for 8 minutes. The temperature should not be allowed to fall below 130 F., nor the concentration of the acid below 20% if the desired dull white appearance is to be obtained. The wire was then washed with cold running Water, after leaving the acid, and was then passed into a sodium cyanide solution, in which it was immersed for 10 minutes. The solution was kept within the limits of 1 to 3 ounces of sodium cyanide per gallon, although these limits are not critical. The cyanide is preferably kept at room temperature but may be warm and may be used in conjunction with current. This cyanide bath was used as a wash to neutralize any acid remaining on the wire and also to leave a protective film on the wire which does not have to be Washed off before the wire enters the cyanide plating bath.

The wire was passed from the cyanid wash into the cyanide copper plater and was plated at 30 amperes/sq. ft. The current density may be considerably higher but a higher amperage is not necessary. Preferably the solution is operated at about 150 F. and kept at an analysis of 30 to 40 grams per liter of copper, 15 to 25 grams per liter of free cyanide, 20 to grams per liter of sodium potassium tartrate, together with carbonate as desired. The pH of the solution should be kept above 11 and it should be free from hypo.

The described process gives a copper coating of 20 to 24 grams per kilogram of wire (0.00075 inch in thickness), but a minimum of about 3 grams or approximately 0.0001 inch is sufiicient to provide an adherent coating. The primary importance of this step is to coat all of the steel with the cyanide deposited copper and if the wire has been properly cleaned it will assume a uniform coat immediately upon entering the plating solution.

The wire is then thoroughly washed and enters the acid copper plating solution. It was plated at about 165 amperes/sq. ft. for 2 hours and 30 minutes in this bath. While the analysis of the solution can vary greatly in the example, it consisted of grams per liter of copper and 75 grams per liter of sulfuric acid. This particular bath combines maximum conductivity and cathode efficiency. The solution must be vigorously agitated with air during the plating. It is preferably maintained at F. Temperatures above F. develop a poor bond between the copper coatings. The presence of nickel, even in amounts as low as 0.2 gram per liter, produces a poor bond. In this bath a coating of 350 grams per liter was applied in the time specified, making a total thickness of 370 grams or 0.0225 inch; The wire Was, therefore, increased to 0.230 inch in diameter and 33.6% of the cross section of the coated wire Was copper.

While current densities as high as 300 amperes/sq. ft. have been used in the acid plating solutionwitheorrespondingdecreaseintimefor a thickness of equal coating, the copper-deposit tends to become more brittle as the current density appproachcs the higher ranges.

After the second plating operation the wire waswashedandwasreadyi'ordrawing. 'Itwas then drawn, using soap as a lubricant with a reduction of approximately per pass. The wireinthlsexamplesuccessivelyreducedtothe following diameters: 0.208, 0.195, 0.175, 0.156, 0.140, 0.125, 0.112, 0.100, 0.090 and 0.081.

The finished wire had a conductivity of 40%, a resistance of 3.97 ohms/1000', and a tensile strength of 1170 lbs (227,000 lbs/sq. in.).

In mother case, wire having a diameter of 0.255 was coated as described to increase its dimeter to 0.293 and was then drawn in successive stages to 0.107. The resulting wire had a 30% conductivity and a tensile strength of 253,- 000 lbs/sq. in.

As another example of the process, which is suitable primarily for smaller wires, the wire is first run through a hot 32% hydrochloric acid bath for 1.25 minutes. The wire, upon leaving the acid bath, must be clean, crystalline in appearance, and silvery white. The acid should be hot and at least 20% hydrochloric acid. If allowed to become dirty, or it used on too much wire, it becomes ineffective and leaves a carbon smudge on the wire. Sulfuric and nitric acids leave such a smudge. Before entering the bath the wire is scraped, for instance with steel wool, and after leaving the solution is wiped with rags, and then washed with water, and again wiped. The wire is then treated with an alkaline solution, for example, an Oakite 42B solution, at the rate of two ounces to a gallon at an advanced temperature, say 180' F. for about a minute. An Oakite solution is essentially an alkaline phosphate. It is then washed and wiped and run into a copper cyanide plating bath. This bath is suitably one containing 48 grams per liter of copper cyanide, grams per liter of free cyanide, containing sodium carbonate as desired.

The solution should be free from ypo. in order to produce as large crystals as possible. A suitable plating density is one of amperes/sq. ft.

Preferably the solution is operated at 150' F. or

thereabouts, and is kept circulating. The amount of copper plated in this bath may be varied, but suitably is from 0.0002 inch upwards in thickness, for example approximately 0.0008 inch, .which may be procured in about 5 minutes under the conditions specified. Even with a hypo-free solution the crystals are very small compared to copper deposited from an acid bath. The plating in cyanide is quite slow so that, owing to reasons of economy, the amount of plating therein i preferably kept small. .Moreover, a layer which is too thick is too brittle to drawproperly.

The wire is then washed in cold water and rinsed in hot water.

The wire may then be washed in a sodium cyanide bath containing about 3 ounces per gallon of NaCN at 150 F. for a short time. washed with water, treated with 5% hydrochloric acid, washed with water and wiped, and is then passed into an acid copper plating bath.

Such a bath is suitably a blue vitriol so ution containing to grams per liter of copper and about grams per liter of sulfuric acid. A suitable plating density is 225 amperesper square foot at a temperature of F. The bath is preferably agitated violently with air during the plating.

with the bath described the amount of copper deposited may be varied substantially at will. Ifasuccessimofcyclesis employedaplating time of to 1% minutes is preferred. In this time approximately 0.0005 inch of copper is deposited. When only a pair of cyclesis employed the thickness of this coating should be within approximately 0.000375 and 0.00075 inch of thickness. But if only two plating baths are used, then the coating may be much thicker.

In carrying out multiple cycles, after removal fromthebaththewireispassedthrougha water wash, then treated with 32% hydrochloric acid, after which it is again washed by running through rags, again passed through an alkaline bath at a concentration of approximately 2 ounces per gallon at a temperature of 180" R,

again washed with water by running through rags, and then again placed in a copper cyanide plating bath.

Thisbathisthesameasthecyanidebath heretofore described, but the product is maintained in it only aboutone minute instead of live, during which time about 0.0001 inch of copper is deposited. The product is then washed with cold water, and then with hot water. The product may then be passed through sodium cyanide solution. containing about 3 ounces per gallon at F. It is then washed with water, in 5% hydrochloric acid for several minutes, and i then washed with water by running through watered rags for several minutes.

The product is then passed into the acid bath, as heretofore described, where it is copper plated for 38 minutes, during which time approximately 0.016 inch of copper is deposited. The product is then washed with water.

The thicknesses of copper given heretofore are upon the entire diameter of the wire and the thickness in each side is, therefore, one-half as much.

During the entire multiple plating operation described, the diameter of the wire increases by about 0.0165 or about 260 to 265 grams copper per kilogram of wire. The coating which is produced in the above described manner is very adherent, and will withstand a bend without breaking or cracking. It will also stand drawing without breaking or cracking.

When only one cycle is employed the cyanide coating may be any thickness from about 0.0002 inch upwards. The acid coating will not adhere to the base metal and therefore the cyanide coat should be enough to provide a suitable base. Ordinarily from 0.0008 inch to about 0.0020 inch is preferred for the coating. The acid coating is then of sumcient thickness to give the desired conductive coating.

The wire is drawn down to final size in several steps. This may be done on three or four pass continuous wire drawing machines employing Carboloy dies. Either steel drawing dies or copper drawing dies may be employed. A preferred drafting procedure is as follows:

The 0.119 wire is first reduced to 0.104, then to 0.085, then to 0.072, then to 0.061, then to 0.051, then to 0.042. These fi ures are the size of the core only. At the end of the finishing speed of the wire is preferably around 375 feet per minute. No unusual precautions are required.

After drawing, the tensile strength of the core will be found to be at least 245,000 lbs/sq. in., as compared to a maximum of about 142,000 lbs/sq. in. heretofore obtainable. The product also has a torsion between 60 and 80 for an 8 inch piece.

. The overall tensile strength of the copper coated wire will be at least 210,000 lbs/sq. inch.

After drawing to final size, the wire may be hot-tinned in accordance with the usual practice, being run through molten tin preferably at a temperature of about 500 F.

The finished wire has a resistance of 16.5 to 17.5 ohms/1000, and a conductance of 30%. It can be bent round its own diameter without breaking or cracking. The thickness of the copper on each side of the 0.045 inch wire was about 0.003 inch in the example given, and is uniform within 0.0004 inch from the average in any single cross section. Much greater thicknesses may be produced if desired.

The copper, when first applied, has a matte finish and is porous. When drawn, however, it is bright, hard, and continuous and maybe bent upon its own diameter.

In all cases the conductivity is at least Instead of the cycles here shown, additional alternatives may be employed, but are unneces- Sary.

. This application is a continuation-in-part of application, Serial No. 238,278, filed November 1, 1938, now Patent No. 2,317,350, Apr. 27, 1943.

The foregoing detailed description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. The method of forming a copper clad wire which comprises cleaning a ferrous wire in a hot clean bath of hydrochloric acid having a concentration not substantially less than to produce a silvery white crystalline appearing surface, electro-depositing upon such surface from the cyanide bath a firmly adherent layer of copper, and electro-depositing upon the cyanide copper a firmly adherent layer of copper from an acid bath.

2. The method of producing a drawn copper clad steel wire having high tensile strength and a conductive copper outer coating which comprises cleaning the steel wire in an acid to produce a silvery white crystalline appearing clean surface thereon, progressively passing the clean wire into an alkaline cyanide copper-plating bath and electroplating thereon an adherent thin coating of copper, removing the wire progressively from the bath. removing residual cyanide solution therefrom, then progressively introducing the wire into an acid copper-plating bath and forming a relatively thick layer of porous matte copper thereon and then drawing the composite copper article substantially to reduce its diameter, thereby altering the porous matte copper to a bright hard continuous electro=conductive coating, the copper being thick enough to produce a conductivity of at least 15% in. the drawn wire.

245,000 lbs. per square inch and having thereon a hard continuous copper coating at least about 0.003 inch in thickness and produced by the method of claim 2.

5. A copper clad steel wire having a conductivity of at least 15% and having a central steel core having a tensile strength of at least 245,000 lbs. per square inch and having thereon a hard continuous copper coating at least about 0.003 inch in thickness and produced by the method of claim 2.

6. The method which comprises cleaning a ferrous wire in a hot clean bath of hydrochloric acid having a concentration of not substantially less than 20 per cent, then progressively passing the clean wire through an alkaline cyanide bath and electrodepositing thereon a firmly adherent layer of copper having a thickness of at least .0001 inch and not more than .0004 inch, cleaning the copper plated wire to remove the cyanide and progressively passing the wire through an acid copper plating bath and depositing thereon -a heavy layer of copper having a thickness of at least .002 inch, the total amount of copper on the wire being sumcient to give a conductivity of over 15 per cent.

ORVILLE E. ADLER.

REFERENCES EDITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,322,494 Merritt Nov. 18, 1919 1,601,982 Romanelli Oct. 5, 1926 61,143 Bernohe Jan. 15, 1867 64,135 Parar Apr. 23, 1867 1,992,244 Schuricht Feb. 26, 1935 2,268,617 Pierce Jan. 6, 1942 2,196,002 Whitney Apr. 2, 1940 2,317,350 Adler et a1. Apr. 27, 1943 FOREIGN PATENTS Number Country Date 12,720 Great Britain of 1849 18 Great Britain of 1855 25,393 Great Britain -1 of 1913 OTHER REFERENCES Blum & Hogaboom, Principles of Electroplating, etc. (1930), 2nd ed., pub. by McGraw-Hill Book (20., N. 2., pp. 149, 150. (Copy in Div. 56.)

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